XBOX live dropout Black Ops (COD)

My son is driving me insane! He has an XBOX 360 and COD Black ops to play on it, it is connected to my rock solid Draytek router (b/g/n) using a G type xbox wireless network adapter. After a more or less random time playing he loses connection, the SYSLOG on the router shows a close connection command - anybody got ideas? The language is terrible (but understandable I guess!)